This kind of outboard motor is disclosed, for example, in Japanese Utility Model Registration No. 2568292 entitled “Exhaust system of Outboard Motor.” An exhaust passage of this exhaust system vertically passes through an exhaust guide. The exhaust passage is cooled by a coolant passage formed within the exhaust guide.
The coolant passage is blocked by a cover formed by a lateral extension of an oil pan provided above the exhaust guide. Since disposed below the engine, the oil pan becomes too large in its entire outer shape as a single component to block the upward opening of the coolant passage, and has poor mountability in blocking the coolant passage.
Next, a marine engine, for example, will be described. A marine engine takes in outside water as coolant for the engine. A coolant jacket is provided around an exhaust passage member to be exposed to high temperature. Outside water is taken into the coolant jacket for cooling the exhaust passage member. The exhaust passage member is an assemblage of a plurality of components such as an upstream exhaust manifold and an exhaust guide connected thereto, for improved productivity. This kind of marine engine is disclosed, for example, in Japanese Patent Laid-Open Publication No, HEI-9-303155 entitled “Exhaust Structure of V-Engine.”
This exhaust structure provides exhaust passages of cylinders directed toward the inside of banks arranged in a V shape, having at each bank an exhaust collecting passage into which the exhaust passages from the cylinders merge. A lower end portion of the exhaust collecting passage is fitted into an inside collar so as to communicate with an exhaust passage of an exhaust guide. The exhaust collecting passage is connected to the exhaust passage of the exhaust guide via an inside rubber hose. The inside rubber hose is hermetically fitted with a fastening band having fasteners for fixing the inside rubber hose to a connecting part of the exhaust passage. A coolant jacket formed on the outer periphery of the exhaust collecting passage communicates with a coolant passage provided in the exhaust guide through a passage formed by the inside rubber hose and an outside rubber hose fitted to an outside collar integrally molded with the inside collar. The outside rubber hose is hermetically fixed to the outside collar via a fastening band having fasteners for fixing the outside rubber hose.
In the above exhaust structure, however, an upstream portion and a downstream portion have double pipes, the band-like connection hose is provided for each connection, and total four portions are fixed by the fastening bands fastened, resulting in poor workability in assemblage. Further, the elastic force of the rubber hoses and the bonding force of the fastening bands are used to resist the pressure of exhaust leaked from mating surfaces of the exhaust connections. Greater the forces, poorer the workability in assemblage.
Further, Japanese Patent Laid-Open Publication No. HEI-10-339162 entitled “Exhaust Structure of Outboard Motor” discloses a connecting structure of an exhaust passage, in which coolant is introduced into a space formed between upper and lower two seals provided at the connection between an upstream exhaust passage and a downstream exhaust passage. In the connecting structure of the exhaust passage of HEI-10-339162, however, the seals abut against walls defining the exhaust passage of the exhaust manifold, and are thus subjected to thermal effect of exhaust heat. Further, the seals are likely to be dislocated in the direction of the exhaust manifold. Furthermore, a sealing structure of a connection between an upstream water jacket and a downstream water jacket is unclear.
A water-cooled V-4 stroke engine for outboard motors is disclosed, for example, in Japanese Utility Model Laid-Open Publication No. SHO-63-128 entitled “Coolant Drain Passage of V-type Vertical Engine for Outboard Motor.”
Further, an exhaust manifold having a coolant jacket for a water-cooled in-line engine outboard motor is disclosed, for example, in Japanese Utility Model Laid-Open Publication No. SHO-58-102725 entitled “Intake/Exhaust Manifold of Internal Combustion Engine for Outboard Motor” and in Japanese Patent Laid-Open Publication No. HEI-09-189221 entitled “Exhaust System for Outboard Motor.”
Recent trend is to use a water-cooled V-4 stroke vertical engine with good fuel efficiency as the size of outboard motors is increased for higher power. This engine has a larger number of components than single or 2- to 4-cylinder in-line vertical engines, resulting in higher manufacturing cost than in-line engines and higher cost of an outboard motor. It is thus desired that the water-cooled V-type 4-stroke vertical engine have a reduced number of components by sharing components to reduce manufacturing cost.
Hereinafter, in terms of the sharing of components, SHO-63-128, SHO-58-102725 and HEI-09-189221 will be studied.
SHO-63-128 “Coolant Drain Passage” has coolant passing through a thermostat returned to an exhaust manifold, without disclosing an art related to the shape of mating surfaces of the exhaust manifold and a cylinder head, or the exhaust manifold.
SHO-58-102725 “Intake/Exhaust Manifold” has a thermostat case with a mating surface positioned above an exhaust connecting opening. When a cylinder head is inverted upside down, a coolant drain passage after inversion becomes a lower portion in the vertical direction. This is not suitable for a vertical engine in which heated coolant moves upward, preventing the use of the same cylinder head in the V-engine.
HEI-09-189221 “Exhaust System” has no passing of coolant at the mating surfaces of the exhaust manifold and the cylinder head, preventing the use of the same cylinder head for a V-engine when passing of coolant is conceived.
Further, during the passing of coolant between one cylinder head in one bank and an exhaust manifold in a V-engine, when coolant flows from a mating surface of the exhaust manifold into a coolant jacket in the cylinder head via a plurality of openings, merging of coolant flows produces interference in the coolant jacket of the cylinder head, preventing smooth flowing of coolant after absorbing combustion heat of the cylinder head, resulting in stagnating coolant in the coolant jacket.
Further, as a cooling system for an outboard motor, Japanese Patent Laid-Open Publication No. SHO-62-20793, for example, discloses a cooling system having a V-shaped auxiliary coolant passage. From the drawings, the auxiliary coolant passage is formed by drilling, and a water pump inlet is provided closer to a forward tilt shaft with respect to two coolant outlets. However, this cooling system forms the auxiliary coolant passages by drilling and has difficulties in processing holes, being complicated and troublesome, and disadvantageous in production.
Furthermore, Japanese Patent Laid-Open Publication No. HEI-09-41967 discloses “Cooling Structure for Outboard Motor” in which branching passages are formed in a lower portion of an oil pan of a V-engine. This cooling structure has the coolant branching passages consisting of the oil pan and a part connected to the lower portion of the oil pan, resulting in increase in the number of components and operation man-hours.